Nonlinear color processing techniques are well known in the prior art such as in NTSC or PAL television. FIG. 1 illustrates an example of standard nonlinear color processing.. A real world image 10, such as a commentator for an Olympic sports event, reflects blue, green and red colors. These colors are detected by a camera 20 by a photodetector 21 which generates linear red, blue and green (R.sub.L, B.sub.L, G.sub.L) signals. Within the camera, the linear red, green and blue signals are gamma adjusted primarily to reduce noise and to prepare the signal for display. The gamma adjustment is performed by taking the 1/g power, where g is the gamma factor (typically 2) of the linear red, green and blue signals, thereby providing what is commonly known as RGB (red, green and blue) color signals. For example, when linear red, blue and green signals are detected by a photon responsive device such as a camera, the photon quantum noise, also known as shot noise, increases as the square of the luminance. That is, shot noise is equal to the square root of the number of photons detected for a given color. By taking the square root of each of the color signals, the amount of shot noise is equivalent for all levels of brightness for each of the colors. Secondly, the eventual display of the RGB signal naturally squares the RGB signals during the electron discharge process.
The nonlinear RGB signals are then translated or converted to a nonlinear YUV signal for data compression by using a well known linear matrix 30. This conversion is performed to provide for a separate luminance signal (Y) and chrominance signals (UV). The Y signal contains the luminance or grayscale for all three colors. The U and V signal carry the chrominance information for all three colors. Due to the high sensitivity of the human eye to luminance detail, the Y signal is typically transmitted or stored using a higher bandwidth transmission or storage technique and may not be compressed or may be slightly compressed according to well known image compression techniques. In addition, due to low sensitivity of the human eye to details in color, the UV signals are typically transmitted or stored using lower bandwidth transmission or storage techniques and are usually highly compressed using well known image compression techniques. The YUV signals may then be stored in analog form on a videotape, laser disk or the like or in digital form on a computer memory, a CD-ROM (compact disk--read only memory) or the like. The YUV signals may also be transmitted in digital form such as on a computer bus or in analog form such as in an NTSC (national television standards committee) transmission. The NTSC transmission process is a result of the movement from black and white television to color television several decades ago. The original black and white or luminance signal is the Y signal. The subsequently added color Signals U and V were added to the original luminance or Y signal. The nonlinear YUV signal is then transmitted or stored on a channel 40. The channel may use well known techniques for image compression as discussed above. The compressed image is then decompressed by the channel and is then received as a nonlinear YUV signal. The nonlinear YUV signal is then translated or converted to a nonlinear RGB signal through a second well known linear matrix 50. The RGB signal is then displayed on a display 60. As mentioned earlier, todays common display processes inherently square the red, green and blue signals thereby providing nearly true or linear red, green and blue output as displayed image 70.
FIGS. 2A-2E illustrate a common problem with today's typical nonlinear color processing techniques. For simplicity of explanation, assume a two color red-green world where the eye is equally sensitive to both colors. In this case there are only RG and YU color signals rather than RGB and YUV. Given a bright red object over a dark gray or red-green background, a scan line is generated by a camera of the background and object would be as shown in FIG. 2A. This includes the red and green signals being gamma adjusted by the camera. The brightness of the red and green signals is dark gray or about 20% across the scan line until the edge of the object is reached. At that point, the green signal drops to black or about 0% luminance while the red signal increases to white or about 100% luminance. As a result of the process described in FIG. 1 including image compression of the U signal, the YU luminance and color signals are received on the channel as shown in FIG. 2B. In this simplified case, Y=(R+G)/2 and U=(R-G) using prior art techniques. The overall luminance or brightness (Y) signal is about a 20% level until the edge of the object is reached where the luminance signal increases abruptly to about a 50% level. This abrupt edge of the luminance signal is due to the typically high bandwidth of the luminance or brightness (Y) signal. The color signal (U), as shown in FIG. 2B, has a gradual or slanted slope rather than vertical or abrupt transition due to the typically lower bandwidth and compression of the U carrier. FIG. 2C shows the received signal from the channel after the YU signal has been converted back to RG where R=Y+U/2 and G=Y-U/2. Note that the average of the R and G, which is the average of Y+U/2 and Y-U/2, is equal to the luminance signal of FIG. 2B as expected. Deviation from the average, as shown by the arrows in FIG. 2C, is equal to the color signal of FIG. 2B as expected. The variation of the R and G signals of FIG. 2C from FIG. 2A is a result of the typically lower bandwidth of the U color signal. FIG. 2D illustrates the displayed signal with the R and G signals being squared by the typical display process. FIG. 2E illustrates the brightness of the viewed image as seen by the user which is the sum of the displayed red and green signals. Note that even though the brightness or luminance (Y) signal was provided the typically full bandwidth for no loss of signal, the resulting brightness of the viewed object has a fuzzy or blurry transition at the object edge. This is due to an undesirable crossover effect of the typically lower bandwidth or compression of the color (U) signal.